To night we are going to have a `Blue Moon'. When did we have it last time?
The second full moon to occur within a given month is called a Blue Moon.
Other factors such as forest fires, volcanic eruptions, and plain old air pollution can cause the moon to take on a bluish glow. This type of thing happened in 1991 when Mt Pinatubo blew its top in the Philippines. In the 1950s forest fires in western Canada caused the same effect in some places, but these had nothing to do with the Blue Moons that we refer to here.
Mathematically, a blue moon occurs, on average, about every 32 months, but in 1999, three occurred in a two month span! The first record of the term was in 1824, but its official use began in 1932 with a reference in the Maine Farmers Almanac. They considered a blue moon as the fourth full moon in a three month season.
In 1946 Sky and Telescope magazine misinterpreted this to mean the second full moon in a given month. Several other sources continued to express the same misinterpretation through the 1980s and that became the definition acc ...more